How Can Reflected Light Modify Solar Gains in a Compact Urban District?

Abstract

Urban sprawl has become a major concern worldwide. The historical solution is the compact urban district, current in the old centers of many European cities. Their compactness presents many advantages that must be preserved for an efficient urban design. However, the compact urban district seems to be more challenging regarding daylight availability (Patriarche Mesure et modélisation de la lumière naturelle dans les canyons urbains. PhD thesis, ENTPE, Vaulx-en-Velin (France), September 9, 2014) and solar gains (Beckers et al. Sustainable building for a cleaner environment. Springer, Cham, 2018). The study here presented has been realized in Rue des Tonneliers, a street of Old Bayonne, a heritage city in the southwest of France. Its compact morphology and high density have deserved an urban retrofitting project enhancing the livability of the district and its energy performance.

The historical city tends to be irregular, and the semantic information necessary to reconstruct it as a case study is usually scarce. For this work, an urban survey through mobile and aerial scanners has been carried out, followed by the construction of a colorized point cloud used as a reference to build an accurate three-dimensional urban model. The semantic information for this case study was obtained by determining the actual reflection coefficients, by means of photographic techniques. This method permits to reproduce an accurate reflection coefficient map of the façades.

The precision of the model geometry and semantics introduces new difficulties at the time of setting up the simulation procedure. It is important to reflect on the correct location of the calculation points taking into account the aimed results, since using a simplified method could lead to false results. A 3D model that accurately reproduces the morphology and semantics of the urban scene is easily modifiable by changing the reflection coefficients or altering the WWR (window to wall ratio). Modifying the actual scenario in order to simulate solar gains over facades may help evaluate the energy efficiency and urban comfort through passive design.

Two different possibilities of urban retrofitting in a compact urban district based on architectural decisions have been explored. The level of detail needed for radiative analysis (solar gains) will be discussed. Therefore, a geometrically and semantically rich 3D model has been recommended for a complete analysis. The result may help to evaluate the energy consumption demand through passive energy methods.